Which of the following is a major advantage of waveguide over coaxial cable for use at microwave frequencies?

At microwave frequencies, standard coaxial cable introduces significant signal attenuation due to dielectric losses and the skin effect on the center conductor. Waveguides overcome this by eliminating the center conductor and solid dielectric material, resulting in exceptionally low losses for high-frequency RF energy. While waveguides are highly efficient at these frequencies, they are certainly not easy or inexpensive to install. They are rigid, require precise plumbing-like connections, and are custom-sized for specific frequency bands. Furthermore, a waveguide cannot practically support a frequency response down to 1.8 MHz. Because a waveguide's physical dimensions must be proportional to the wavelength of the signal, a waveguide designed for 1.8 MHz would be impractically massive.